In order to improve the energetic efficiency of internal combustion engines, in particular in vehicle applications, it is possible to utilize heat energy, which is contained in the exhaust system of the internal combustion engine. The heat contained in the exhaust system can be converted into electric energy for example with the help of thermoelectric generators. To this end, heat exchangers of the type mentioned at the outset are employed, which comprise at least one thermoelectric generator having a hot side and a cold side. In addition or alternatively, heat exchangers can be employed for utilizing the heat energy contained in the exhaust system in order to transfer the heat from the exhaust system, which then serves as heating medium, in order to thereby heat a passenger interior or in order to evaporate the cooling medium, which then serves as operating medium within a Rankine cycle process. A heat exchanger, which comprises at least one thermoelectric generator, furthermore comprises at least one heating tube for conducting a heating medium, which is arranged on at least one hot side of such a thermoelectric generator, and at least one cooling tube for conducting a cooling medium, which is arranged on at least one cold side of such a thermoelectric generator. Practically, it can be provided here that within the heat exchanger of the at least one thermoelectric generator the at least one heating tube and the at least one cooling tube are stacked on top of one another in a stacking direction, thus forming a tube stack, in which the respective thermoelectric generator, the respective heating tube and the respective cooling tube extend parallel to one another in a longitudinal direction of the tube stack.